Optical glass, prefabricated member and optical element

According to the present invention, the optical glass having a refractive index (nd) and an Abbe number ([nu] d) within required ranges and having high devitrification resistance can be obtained at a lower price. The optical glass contains, in mol%, 5.0% or more and 55.0% or less of a B2O3 component and 5.0% or more and 30.0% or less of a La2O3 component, the sum of moles (Nb2O5 + WO3) being less than 10.0%, and has a refractive index (nd) of 1.70 or more and an Abbe number ([nu] d) of 25 or more and 50 or less. The optical glass can be used for various optical elements and optical design. 本发明能够以更低廉的价格得到一种折射率(nd)以及阿贝数(νd)均在所要求的范围内，并且耐失透性较高的光学玻璃。所述光学玻璃，以摩尔％计算，含有B2O3成分5.0％以上55.0％以下，La2O3成分5.0％以上30.0％以下，摩尔之和(Nb2O5+WO3)小于10.0％，并且具有1.70以上的折射率(nd)，25以上50以下的阿贝数(νd)。该光学玻璃，可使用于各种光学元件以及光学设计。